Using done() callback in Glitch

Using done() callback in Glitch
0

#1

Hello!

I’ll try and make this short. So I’ve been going through the Mongoose tutorials and I am doing ok, but I feel like my biggest hangup is the whole done() callback convention. The tutorials have the basic explanation:

_// **Note**: GoMix is a real server, and in real servers interactions with_
_// the db are placed in handler functions, to be called when some event happens_
_// (e.g. someone hits an endpoint on your API). We'll follow the same approach_
_// in these exercises. The `done()` function is a callback that tells us that_
_// we can proceed after completing an asynchronous operation such as inserting,_
_// searching, updating or deleting. It's following the Node convention and_
_// should be called as `done(null, data)` on success, or `done(err)` on error._
_// **Warning** - When interacting with remote services, **errors may occur** !_

_// - Example -_
_// var someFunc = function(done) {_
_//   ... do something (risky) ..._
_//   if(error) return done(error);_
_//   done(null, result);_
_// };_

I just don’t really understand where that is coming from. For example we have in challenge 6 the following:

var findOneByFood = function(food, done) {

  Person.findOne({favoriteFoods: food}, function(err, data) {
    if (err) return done(err);
    return done(null, data);
  });
  
};

That works fine and everything, but I’m not really sure what’s going on when I am using the done callback. My understanding is that I would literally be placing some callback function (assigned somewhere else?) in place of the “done.” But I feel like that’s wrong and it’s a real callback coming from somewhere else. For example, why is it done(null, data) ? Where are those arguments getting established?

I’ve actually done a while mongoDB course on their website so the concepts of making queries and everything seem very simple, but I just feel lost with how that callback is being used/implimented and tried looking elsewhere online but can’t find anything! Help! (Please :slight_smile:)